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December 16-17, 2020 Winter Storm Obs/Nowcasting


WxUSAF
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2 hours ago, ovechkin said:

Going to top out at 43-44-45, clouds already start to build, will keep lows well above freezing (inside the beltway) and then we see white rain for an hour.  This show airs more than Shawshank Redemption on cable.  Both shows end standing in the rain. 

Most of the day was 39-42 and your observation from 11am that this afternoon would torch because it was 40 at 11am was incorrect. Save the despondency for banter 

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Just now, Eskimo Joe said:

You never get above freezing. It looks like you stay snow the entire event. The mix line walks around the topside of I-695 but you flirt with probably a couple hours of solid snow rates and don't stop snowing until sometime just before sunrise Thursday.

Awesome. I like that very much, thank you!

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1 minute ago, WxUSAF said:

It is sssuuuuccchhhh a fine line for us.  12z was nearly identical actually.  We're a long hike from heartbreak or happiness in one direction or another.  

Maybe a few more model cycles gets the cold to hold on just a bit longer for us. 

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      It's worth noting that in the CAMs (especially the NAM nest) that turn central and north-central MD over to sleet for a long duration, the warm layer is up around the 750 or 700 mb level.    The GFS is typically very poor at capturing those warm layers if they're well above, say, the 850 level.    PSU made a reference earlier to the March 2017 storm in which the GFS missed forecasting most of the sleet because it kept things much colder aloft.     It isn't the same GFS now, but I would not be surprised if this weakness holds.

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1 minute ago, high risk said:

      It's worth noting that in the CAMs (especially the NAM nest) that turn central and north-central MD over to sleet for a long duration, the warm layer is up around the 750 or 700 mb level.    The GFS is typically very poor at capturing those warm layers if they're well above, say, the 850 level.    PSU made a reference earlier to the March 2017 storm in which the GFS missed forecasting most of the sleet because it kept things much colder aloft.     It isn't the same GFS now, but I would not be surprised if this weakness holds.

Yeah, I said that about the 12z GFS as well.  I don't buy the isothermal skew-t's it's showing.  Think there's a much larger area of sleet between the snow and rain.  And I think we're probably in it.  Hoping we avoid much rain...

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The 18z NAM 3k, GFS, and RGEM all advertise a quick, say 3 hour, CCB on the backside for Frederick, Carroll, Howard, Baltimore, and Harford counties. It's all snow with crashing temps that might deliver a surprise to the usual suspects. Not something to bank on, but it would be snow on top of IP/ZR which would be guaranteed to stick.

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32 minutes ago, mappy said:

That makes sense. 

I remember that March 2017 storm. Got some snow before a big thump of sleet. yippee. 

I mentioned march 2017 yesterday when things were trending the wrong way with this one. We were expecting a big dump and got a long period of sleet at the height of the storm. We did switch back to snow but that was during the day in march with temps in the low 30's so we only picked up up a couple more inches even though it snowed moderately for most of the day. At least with this storm if we get snow on the backside it will be at night with colder temps. If we can switch back to all snow by 3z then 3-6 is a real possibility.

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19 minutes ago, WxWatcher007 said:

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Seriously though, good luck tomorrow. I don't know your exact location but hopefully the front end produces for as many people as possible tomorrow. 

Thanks reaper man.  My exact location is near Fail Town.   But west of the fall line so whatever.  I’ll get a little something to brighten the grass.  Enjoy having you here!  

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2 minutes ago, WxUSAF said:

Yeah, I said that about the 12z GFS as well.  I don't buy the isothermal skew-t's it's showing.  Think there's a much larger area of sleet between the snow and rain.  And I think we're probably in it.  Hoping we avoid much rain...

             Agreed on all counts.    The GFS typically shows way too small of a small transition zone between rain and snow.      I do think that eastern Howard may get a decent sleet mess out of this.

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1 minute ago, high risk said:

             Agreed on all counts.    The GFS typically shows way too small of a small transition zone between rain and snow.      I do think that eastern Howard may get a decent sleet mess out of this.

Here's hoping...

 

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9 minutes ago, WEATHER53 said:

Most of the day was 39-42 and your observation from 11am that this afternoon would torch because it was 40 at 11am was incorrect. Save the despondency for banter 

Despondency? Hardly- more humor, but your point is still a good one and well taken. You a great forecaster and know our climate well. My point was less about conditions at onset  ( I think most agree snow at onset) vs how quickly we would turnover. Especially inside the beltway. Yet to be determined. Hope I am wrong! 

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1 minute ago, ovechkin said:

Despondency? Hardly- more humor, but your point is still a good one and well taken. You a great forecaster and know our climate well. My point was less about conditions at onset  ( I think most agree snow at onset) vs how quickly we would turnover. Especially inside the beltway. Yet to be determined. Hope I am wrong! 

Let this post be an example of how we should all respond to ambiguity.

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